Thermodynamics of the binding of cytotoxic protoberberine molecule coralyne to deoxyribonucleic acids.

The binding thermodynamics of the interaction of protoberberine molecule coralyne to various DNAs have been investigated. Thermodynamic data revealed that the binding was enthalpy driven in GC rich DNA and GC polynucleotides while the same was favored by both negative enthalpy and positive entropy changes in the AT rich DNA and AT polymers. Parsing the free energy change of the binding in terms of polyelectrolytic and nonpolyelectrolytic contribution showed the involvement of major contributions from the later. The heat capacity change (DeltaC(p) degrees ) for the binding of coralyne to calf thymus DNA and Micrococcus lysodeikticus DNA was - 147 and - 190cal/(mol K) respectively. The binding data in these systems also showed significant enthalpy-entropy compensation confirming the involvement of multiplicity of weak non-covalent interactions in agreement with the negative heat capacity data. Circular dichroic studies revealed that the binding was accompanied by moderate conformational change of B-form structure and more importantly the achiral alkaloid molecules acquired strong induced optical activity. These results contribute to the understanding of energetics of coralyne-DNA complexation that will guide synthetic efforts of medicinal chemists for developing better therapeutic agents.